1. Field of the Invention
The present invention relates to an imaging device including a photosensitive body, a developing unit, and so on, used for an image forming apparatus, such as a copying machine, a facsimile, a printer, and the like. The present invention also relates to an image forming apparatus equipped with the imaging device, and further relates to a process cartridge which serves as the imaging device.
2. Description of the Related Art
In such an image forming apparatus, a latent image is formed on a photosensitive body which serves as a latent image carrying body, and then developed by using powder toner carried on a developing roller which serves as a developer carrying body. A part of the developing roller is exposed from an opening formed on a casing of a developing unit so that the exposed part of the roller faces to the photosensitive body. As a result, the toner may be scattered inside and outside of the apparatus to stain or pollute the surroundings. As one of the methods for suppressing or reducing such a staining or pollution caused by toner scattering, a method has been developed in which toner is collected by an air flow. In particular, widely known is a method in which a duct provided with a suction port is arranged around a developing roller where toner is scattered frequently, thereby collecting the toner intensively.
In the image forming apparatus disclosed in Japanese Patent Application Laid-open No. H6-059565, an air flow unit that collects scattered toner by generating a suction air flow is provided downstream of a developing area in a rotational direction of a photosensitive body. The developing area is an area where a developing roller of a developing unit faces to the photosensitive body. The air flow unit includes a duct that serves as a path of the air flow and that extends in the longitudinal direction of the developing roller, and a pump that is provided to one end of the duct in the longitudinal direction and that generates the air flow. On the wall surface of the duct, a first suction port and a second suction port are formed along the rotational direction of the photosensitive body. The first suction port is located in the vicinity of the photosensitive body and opened toward the surface of the photosensitive body. The second suction port is located upstream of the first suction port in the rotational direction of the photosensitive body. The second suction port is located apart from the photosensitive body and opened toward the developing area. The pump generates the suction air flow in the duct, thereby sucking and collecting the scattered toner around the photosensitive body into the duct from the first suction port and the second suction port. Furthermore, the opening area of the first suction port is smaller than that of the second suction port. By making the opening area of the first suction port smaller than that of the second suction port, it is possible to suck the scattered toner from the first suction port with suction force larger than that of the second suction port. With this configuration, the second suction port having smaller suction force sucks a small amount of toner scattered at a position or area distant from the surface of the photosensitive body first. Subsequently, the first suction port arranged close to the surface of the photosensitive body and having larger suction force sucks a large amount of toner scattered in the vicinity of the surface of the photosensitive body. Thus, the air flow unit distributes the suction force to each suction port appropriately, thereby performing the suction efficiently.
The first suction port is arranged very close to the surface of the photosensitive body in order to suck a large amount of scattered toner from the first suction port in the vicinity of the surface of the photosensitive body. As a result, it is difficult to manage the gap between the first suction port and the surface of the photosensitive body. If the first suction port is arranged excessively close to the surface of the photosensitive body, the wall surface of the duct forming the first suction port comes into contact with the surface of the photosensitive body because of vibrations or the like generated during the rotation of the photosensitive body. As a result, there is a problem in that the surface of the photosensitive body is damaged or scratched.